Pebble heater apparatus



Filed Aug. 24, 1948 R. BERKEMEYER PEBBLE HEATER APPARATUS ill 2 SI'IEETS-Sl-IEET 2 .INVENTOR. RBERKEMEYER A TTORNE YS Patented Oct. 21 1952PEBBLE HEATER APPARATUS Robert Berkemeyer, Bartlesville, kla., assignorto Phillips Petroleum Company, a corporation of Delaware ApplicationAugust 24, 1948, Serial No. 45,901

11 Claims.

This invention relates to a solid material feeder. In one of its morespecific aspects, it relates to a pebble feeder in pebble heaterapparatus. In another of its more specific aspects, it relates to animproved method for controlling the speed of pebble flow through pebbleheater apparatus.

Thermal treating and conversion processes which are carried out inso-called pebble heater apparatus utilize a flowing mass of solid heatexchange material which mass is heated to a high temperature by passinghot gas therethrough in a first direct heat exchange step and is thencaused to contact a second gaseous material furnishing heat to thesecond gaseous material in a second direct heat exchange. Theconventional pebble heater apparatus generally com prises two chamberswhich may be disposed in substantially vertical alignment. The solidheat exchange material is introduced into the upper portion of the firstor upper chamber. That material forms a moving or fluid bed of solidheat exchange material which flows downwardly as a contiguous massthrough the chamber in direct heat exchange with hot gaseous heatexchange material. The solid heat exchange material is heated to arelatively high temperature in the heat exchange and is then passed to asecond chamber in which the hot solid heat exchange material is causedto contact a second gaseous material in a second direct heat exchangerelation furnishing heat for the treatment or conversion of the gaseousmaterial.

Flow of solid heat exchange materials through pebble heater apparatus isin many instances quite difficult to control. VIhen the apparatus isutilizedfor the purpose of converting hydrocarbons, the flow rate ofpebbles through the pebble heater apparatus is very critical to theefficient conversion of the hydrocarbons. It is only by the closestcontrol of the pebble flow rate that it is possible to prevent theover-conversion of the gaseous hydrocarbons by reason of excessivetemperatures Within the conversion chamber, or to prevent thunder-conversion by reason of insufilcient temperatures within theconversion chamber. The flow rate of solid material has heretofore beenpartially controlled by the utilization of screw type conveyors disposedat any number of various positions. Flow controllers of this type, asheretofore utilized, have had very narrow limits of variance of the rateof pebble flow. Screw type conveyors which have hereto- .fore beenconventionally used for controlling the flow of solid materials havebeen constructed so that the helix about the inner stem has a relapebbleheater apparatus.

tively fiat pitch. In order to completely stop the flow of the solidmaterial, itis necessary that the angle of pitch of the helix be lessthan the in heating apparatus such as pebble heaters to control the rateof .flow of solid material so that it moves at one rate of. flow throughthe apparatus over a given period of time for a given conversion and atother times considerably higheror lower rates of flow maybe desirable.

An object of this invention is to provide an improved method forcontrolling theflow of solid materials through a solid material system.Another object is to provide an improved method for controlling the rateof flow of solid materials through a solid material system. Anotherobject is to provide a means for controlling the rate of flow of pebblesthrough pebble heater apparatus.

Another object is to provide an improvedmethod for controlling the rateof flow of pebbles through Another object f the invention is to providemeans for slowing and stopping the flow of solid material in contactchambers. Another object is to provide a device capable of increasingthe rate of flow of solid material in a contact chamber above the rateof flow obtained by gravity. Other and further objects and advantageswill be apparent upon study of this disclosure andthe acco mpanyingdrawmg.

Solid heat exchange materialwhich is conventionally used in pebbleheater apparatus is generally called pebbles. The term pebbles as usedherein denotes any solid refractory material of fiowable size and formhaving the capacity to carry large amounts of heat from the pebble lheater chamber through the gas heating or conversion chamber withoutrapid deterioration or substantial breakage. Pebbles conventiflnallyused inpebble heater apparatus are substantially spherical and rangefrom about inch to about 1 inch in diameter. In a high temperatureprocess, pebbles having a diameter between /4 and nch are preferred. Thepebbles must be formed of a refractory material which will withstandtemperatures at least as high as the highest temperature attained in thepebble heating chamber. The pebbles must also be capable OfVlithstandingtemperature changes within the apparatus. Refractory materials, such asmetal alloys, ceramics, or other material having the properties abovedescribed may be utilized to form such pebbles. Silicon carbide,alumina, periclase, beryllia, stellite, zirconia, and mullite may besatisfactorily used to form such pebbles or may be used in admixturewith each other or with other materials. Pebbles formed of suchmaterials, when properly fired, serve very well in high temperatureoperations, some withstanding temperatures up to about 3500 F. Pebbleswhich are used may be either inert or catalytic when used in anyselected process.

Understanding of the invention will be facilitated upon reference to thediagrammatic drawing in which Figure 1 is a vertical partial section ofa solid material feeder embodying the invention. Figure 2 is a verticalpartial section of a solid material feeder embodying a modification ofthe invention. Figure 3 is a schematic view of a pebble heater apparatusshowing the preferred positioning for a solid material feeder of thisinvention.

In Figure 1, solid material feeder II comprises a substantiallyvertically disposed shell I2 which is formed by upper and lower sectionsit and It, respectively. Solid material inlet conduit I5 extends throughthe top of shell I 2 and extends substantially coaxially a part of thedistance through the chamber within shell I2. Solid material outletconduit I8 provides communication between the lower portion of a gasheating, treating, or conversion chamber and solid material inletconduit I5. Outlet conduit I6 and inlet conduit I5 may be joined at apoint II and rigidly retained in place by fastener means, such as boltsI8. Screw type conveyor I9 comprises helix 2I which is mounted on hollowstem 22 and is disposed within conduit I5 so as to extend between stem22 and the inner circumference of conduit I5, thereby closing conduit I5to solid material flow except upon helix 2! about stem 22. Conduitmember I6 is provided with a bearing member 23 in its upper wall. Ringbearing member 24 is rigidly afiixed about the periphery of stem 22 andsupports screw type conveyor I9 within conduit I5, bearing upon bearingmember 23. Also rigidly affixed about the periphery of stem 22 is pulleymember 25. Support member 26 extends upwardly from conduit I6,Reversiblevariable speed motor 2! is mounted on support member 26 sothat the drive wheel mounted on its rotor shaft is opposite pulleymember 25. A belt member provides an operative connection means betweenthe drive wheel and pulley, whereby rotation of conveyor i9 is provided.Table support member 28 extends coaxially through stem 22 and issupported at its lower end by bearing member 29 which is in turnsupported by spider arms 3i extending between the walls of solidmaterial outlet conduit 32 in the lower portion of shell I2 and bearingmember 29. Support member 28 is axially supported at its upper end bybearing member 33 which is in turn supported by support member 26.Rigidly mounted on table support member 28, below the outlet from solidmaterial inlet conduit I 5, is rotatable table balile 34. Table supportmember 28 may be raised or lowered by elevation means which may comprisea Selsyn motor 35 which may have a pinion mounted on its rotor shaft ormay comprise a motor of the type which is conventionally used to operatelarge valves. The upper end of support member 23 is prevented fromrotating by a key member in bearing 33 which slides in keyway 36. Thenon-rotatable portion of table support member 28 is connected to therotatable portion of the table support member by thrust bearing 31.Pulley member 33 is slidably mounted on table support member 28 and isprevented from turning thereon by a key in pulley 33 which slides inkeyway 39. Pulley member 38 is maintained in position by a retainermember 4| which extends from support member 25, Table support member 28is allowed to slide through pulley member 33 in response to motor 35.Variable Speed motor 42 is supported on support member 26 and isequipped with a drive wheel on its rotor shaft, the drive wheel beingpositioned opposite pulley member 38. A belt member provides anoperative connection means between the drive wheel of motor 42 andpulley member 38.

In the operation of the device shown in Figure 1, solid material, suchas pebbles, enters feeder I! through inlet conduit I5 and flowsdownwardly around stem 22 over helix 2!. The conveyor shown in Figure lis a righthand helix and as it is rotated in a clockwise directionpebble flow through conduit I5 is accomplished. As the rate of rotationof conveyor IE! is increased or decreased, the flow of solid material,such as pebbles, through conduit I5 is likewise proportionatelyincreased or decreased until the rotation of conveyor IQ is stopped atwhich time the rate of solid material fiow through conduit I5 is onlythat provided by gravity over the inclined surface of theccnveyor. Inone type of operation, conveyor I9 may be reversed in its direction ofrotation and may in that manner approach the function of a screw typeelevator. The reverse rotation of conveyor i9 may be brought to such arate that it will bring about a complete stoppage of solid material flowthrough conduit I5. Complete control of solid material flow may becontrolled in that manner in accordance with one of the variablephenomena of gas heating, treating, or converting.

Table 34 is spaced a predetermined distance below the outlet end ofconduit I5, thereby providing a baflle means for solid material flowingdownwardly through conduit I5. Table 34 is preferably spaced at such adistance below conduit I5 that the solid material which piles up on thetable forms a cone, the apex angle of which is small enough that theslope of the sides of the cone slightly exceeds the angle of repose ofthe solid material utilized in the system. Each of the motors 21!, 35and 42 are preferably regulated in accordance with one or" the variablephenomena of gas heating, treating, or conversion in the system. Asynchronizer control Gil is provided to synchronize the operation of thethree motors.

Conveyor [9 may be driven by motor 21 at such a rate and in such adirection as to provide the desired rate of how or" solid materialthrough the solid material system. In many cases, it may be desired tomaintain a sharp line of control over the temperature within the solidmaterial system. In some cases, total control of solid material flowrate by conveyor It which is operated in accordance with one of thephenomena of gas heating, treating, or conversion may have a tendency toover-control the flow rate and suddenly throw the phenomena of heating,treating, or conversion too far in the opposite direction. It may bedesirable, therefore, to utilize bafiie table 34 as a check orcounter-control. Table 3 1 may, therefore, be spaced from the end ofconduit I5 in accordance with another of the phenomena of gas heating,treating, or conversion. In that manner, if the rate of rotation ofconveyor I9 should be changed so suddenly as to cause the conditions ofheating, treating, or conversion to fall out ofline with the desiredresults, the synchronizer control 40 may cause motor 35 to operate inaccordance with another of the phenomena. of gas heating, treating, orconversion so as to counteract a part of the change in variablephenomena by reason of the change of rate of rotation of conveyor I9.

Another method in which feeder II may be operated is to regulate therate of flow of solid material through the solid material system byregulating the rotation of conveyor I9 in accordance with one of thephenomena of gas heating, treating, or conversion, A predetermined rateof rotation range may be set for the conversion and upon that rate beingreached, the synchronizer control may cause motor 35 to shift tablebaiile 3t so as .to relieve conveyor IQ of a partial amount of itscontrol of the solid material flow rate. Conveyor I9 would thereupon bevaried within its predetermined rotation rate by the synchronizercontrol.

An even sharper line of control may be accomplished by the apparatus ofthis invention. The speed of rotation of conveyor I3 may be varied inaccordance with one of the variable phenomena of gas heating, treating,or conversion. Table 34 may be spaced from the end of conduit I5 inaccordance with another of the above mentioned variable phenomena andtable M may be rotated by drive member 42 at a rate in accordance withyet another of the variable phenomena above mentioned. By this method ofoperation three variable phenomena may be utilized as checks against oneanother in controlling the solid. material iiow rate through the solidmaterial system. The additional feature of control of this method, 1.e., rotation of table baffle 34, would provide a greater flow of solidmaterial over table 34 than the flow which would be secured for a givenposition of baffle 34 if it was not rotated. It will thus be seen thatif conveyor I9 should over-control in one direction and the spacing oftable 34'. should cut back a slight de-- gree too far in the oppositedirection, it would be possible to moreaccurately check the flow :rateof the solid material by rotating table 34, thus partially eliminatingone chance for error and providing a finer line of control for solidmaterial flow through the solid material system.

The device shown in Figure 2 of the drawing is similar to that shown inFigure 1. Solid material feedcr' II comprises shell I2 which is made upof upper and lower sections I3 and Id, respectively. Solid materialinlet conduit I5 extends through the top of section I3 and is connectedto solid material outlet conduit it which extends from a solid materialsystem similarly to the device shown in Figure l. The connection betweenconduits I5 and It at point I? may be made by bolts Ill, also similarlyto the connection made in Figure 1. Conveyor i9 comprises helix ZI whichextends between a stem 22 and the wall of conduit I5. Stem 22 is hollowin at least its lower portion and extends upwardly through conduit i5and through the wall of conduit It. Bearing member M, which is rigidlyaflixed to the circumference of stem 22, supports stem 22 as it bears onbearing 23 of conduit IE. Pulley member 255 is rigidly aifixed to stem22 and is driven by a belt member which opcratively connects the pulleywith adrive wheel on motor El. In the device shown in Figure 2 of thedrawing, table support member 28 extends upwardly through the wall ofsolid material outlet conduit .let conduit I6.

32 and into the hollow portion of stem 22. Sub port member 28 issupported laterally by bearing member 29 which is in turn supported byspider arms 3i which extend between the walls of conduit 32 and bearingmember 29. The lower end of table support member 28 is threadablyretained in guide member 45 which is in turn supported by support frame46 extending from solid material outlet conduit 32. Pulley member 38 isslidably retained on table support member 28 by a key moving in keyway39 in table support member 28. Pulley 33 is retained in position byretainer frame 41. Pulley member 38 is driven by a belt member whichoperatively connects pulley member 3b with a drive wheel mounted on therotor shaft of variable speed motor 42. Hand wheel is is provided on thelower end of table support member 28, thus providing drive means forspacing table baille 34 from the outlet end of conduit I5. The lower endof table support member 28 is connected to rotating portion of tablemember 28 by thrust bearing member 31.

The operation of the device shown in Figure 2 of the drawing is similarto that shown in. Figure 1, the main diiierence being that the spacingand driving of table baflie is accomplished from below feeder II ratherthan from above. The manual adjustment, 1. e., hand wheel 48, isprovided for spacing table bailie 34 from com duit I5.

In the device shown in Figure 3 of the drawing, a pebble feeder of thisinvention has been utilized in connection with pebble heater apparatus.Pebble heating chamber 5I communicates with gas heating chamber 52through pebble throat 53. Pebbles are injected into pebble heatingchamber 5| through pebble inlet conduit 5.4 in the upper end portion ofchamber 5I Combustible material is injected into chamberbl through inletconduit 55 and is burned so as to form combustion gases within chamberiii to heat the contiguous, downwardly flowing mass of pebbles therein.Gaseous effluent material is removed from chamber 5i through effluentoutlet conduit 55. The heated pebbles enter chamber 52 throughcommunicating throat 53, maintaining the contiguous flow of pebblesdownwardly through chamber 0.? and out of chamber 52 through outletconduit IE. Gaseous material which is thereby heated, treated, orconverted, is injected into chamber 52 through inlet conduit 5'! andpasses upwardly through the contiguous mass of heated pebbles in chamber52. ,Eiiiuent materials are removed from chamber52 through efiluentoutlet conduit 53. If the temperature of pebbles in chamber 52 is toolow, insufiicient heating, treating, or conversion of the gaseousmaterials may be accomplished. On the other hand, if the pebbles inchamber 52 are too hot the gaseous materials may be over-heated,treated, or converted. It will thus be seen that with a relativelyconstant rate of heating pebbles in chamber 5!, it is very necessarythat the flow rate of pebbles through pebble heater apparatus be rigidlycontrolled. Some of the variable phenomena upon which control of therate of pebble flow may be based are the temperature differentialbetween the pebble inlet and outlet of chamber 52, the gravity ofeiiluent material taken at eiiluent outlet conduit 58 when chamber 52 isutilized as a conversion chamber, the temperature of effluent materialtaken from effluent outlet conduit 58, and the temperature of pebblesremoved from chamber 52 through pebble out- Control lines extendfromftherinocouples at GI and gravity measuring means at 62, positionedat points at which the variable phenomena may be measured within chamber52 to synchronizer control 59. Control lines also extend from controller59 to motors 35, 42, and 27, which regulate the position, rate ofrotation of the table baifle, and rate and direction of rotation of thescrew conveyor. Flow of pebbles through conduit It is thereby controlledby solid material feeder H. Pebbles which flow downwardly from feeder lI through pebble outlet conduit 32 are picked up by elevator means 5!and are passed upwardly to pebble inlet conduit 54 through which theyare injected into the upper portion of pebble heater chamber 5!.

Synchronizer controllers, such as controller 59 variable speed motors,such as motor 42; and reversible-variable speed motors, such as motor27, are in common use and are available in commerce. A detaileddescription thereof is therefore deemed unnecessary. A controller suchas the Atcotran control of the Automatic Temperature Control Company maybe used to control the speed and direction of rotation of motors 2i and42 and the direction and extent of movement of motor 35.

Treating and conversion processes in pebble heater and other solidmaterial apparatus ordinarily require the addition of heat. Gas heatingchamber, as recited in the claims, is deemed to include gas treating andconversion chambers.

As will be evident to those skilled in the art, various modifications ofthis invention can be made or followed in the light of the foregoingdisclosure and discussion without departing from the spirit or scope ofthe invention.

I claim:

1. An improved pebble heater apparatus which comprises in combination asubstantially vertically disposed closed pebble heater chamber, saidchamber having a pebble inlet and an effluent outlet conduit in itsupper end portion, and a gas inlet and a pebble outlet in its lower endportion; a closed gas heating chamber having a pebble inlet and aneffluent outlet in its upper end portion and a. gas inlet and a pebbleoutlet in its lower end portion, said gas heating chamber being insubstantially coaxial alignment with said pebble heating chamber andsaid pebble inlet of said gas heating chamber communicating with saidpebble outlet of said pebble heating chamber; a pebble feeder whichcomprises in combination an outer shell, a pebble inlet conduitcommunicating with the pebble outlet conduit of said gas heating chamberand extending downwardly into the chamber within said shell, a screwconveyor rotatably mounted in said pebble inlet conduit on a hollow stemwhich extends upwardly through the upper end wall of said shell, tablesupport means rotatably extending coaxially through and out of each endof said hollow stem, a table rigidly mounted on said support means andspaced below the outlet end of said pebble inlet conduit, elevationmeans operatively connected to the upper end portion of said tablesupport means, reversible-variable speed rotation means operativelyconnected to said screw conveyor, and a pebble outlet conduit in thelower portion of said shell; gravity measuring means operativelyconnected to said eflluent outlet of said gas heating chamber and saidelevation means; first temperature measuring means in the pebble outletof Sa d gas heating chamber and operatively connected to saidreversible-variable speed rotation means; and elevator means connectedat its lower end to said pebble outlet conduit of said pebble feeder andat its upper end to said pebble inlet conduit to said pebble heaterchamber.

2. An improved method of regulating the rate of flow of pebbles throughpebble heater apparatus which comprises the steps of removing saidpebbles from the lower end of a gas conversion zone of pebble heaterapparatus as a contiguous pebble stream; passing said pebble stream intoa pebble flow control zone of a pebble feeder zone; mechanically feedingsaid pebble stream through a tortuous path in said flow control zone;regulating the velocity of said pebble stream in said control zone inaccordance with the temperature of pebbles at the pebble outlet of saidgas conversion zone; regulating the size of the communication spacebetween a pebble collection zone of said pebble feeder zone and saidcontrol zone in accordance with the gravity of efiluent material fromsaid gas conversion zone taken at an eflluent outlet zone in the upperportion of said gas conversion zone, whereby the volume of pebble flowthrough said pebble feeder zone is controlled; additionally controllingthe rate of distribution of pebbles from said control zone to saidcollection zone in accordance with the temperature of effluent fromsaid'gas conversion zone taken at said effluent outlet zone in the upperportion of said gas conversion zone; and passing said pebbles from saidcollection zone through an elevation zone to a pebble heater zone ofsaid pebble heater apparatus.

3. An improved method of regulating the rate of flow of pebbles throughpebble heater apparatus which comprises the steps of removing saidpebbles from the lower end of a gas conversion zone of pebble heaterapparatus as a contiguous pebble stream; passing said pebble stream intoa pebble flow control zone of a pebble feeder zone; mechanically feedingsaid pebbles through the length of said pebble flow control zone at arate variable in response to one of the variable phenomena of gasconversion in said gas conversion zone; controlling the size of a pebbleoutlet zone from said pebble flow control zone in response to another ofthe variable phenomena of gas conversion in said gas conversion zone;varying the rate of pebble removal from said pebble flow control zone inresponse to still another variable phenomena of gas conversion in saidgas conversion zone; and passing said pebbles upwardly from said pebblefeeder zone through an elevation zone and downwardly through a pebbleheating zone to said gas conversion zone.

4. The method of claim 3, wherein the rate of mechanically feeding ofpebbles through the length of said pebble flow control zone iscontrolled in response to the temperature of pebbles at the pebbleoutlet of said gas conversion zone.

5. The method of claim 3, wherein the size of the pebble outlet zonefrom said pebble flow control zone is controlled in response to thegravity of efiluent material from said gas conversion zone.

6. The method of claim 3, wherein the rate of pebble removal from saidpebble flow control zone is controlled in response to the temperature ofeffluent material from said gas conversion zone.

'7. The method of claim 6, wherein the rate of mechanical feeding ofpebbles through the length of said pebble flow control zone iscontrolled in response to the temperature of pebbles at the pebbleoutlet zone of said gas conversion zone.

8. The method of claim 3, wherein the rate of mechanically feeding ofpebbles through the length of said pebble flow control zone iscontrolled in response to the temperature of pebbles at the pebbleoutlet zone of said gas conversion zone; and the size of the pebbleoutlet from said pebble flow control zone is controlled in responseconversion zone.

9. The method of claim 3, wherein the size of the pebble outlet zonefrom said pebble flow control zone is controlled in response to thegravity of efliuent material from said gas conversion zone; and the rateof pebble removal from said pebble fiow control zone is controlled inresponse to the temperature of eflluent material from said gasconversion zone.

10. The heater apparatus of claim 1, wherein second temperaturemeasuring means are provided in said efiiuent outlet of said gas heatingchamber, and rotation means are operatively connected to said tablesupport means and said second temperature measuring means.

11. A solid material feeder which comprises in combination an outershell, a solid material inlet conduit extending through the upper endportion of said shell and downwardly into the chamber within said shell;a solid material outlet conduit extending downwardly from the lower por-10 to said first shaft and extending outwardly to the wall of saiddownwardly extending conduit portion; first drive means operativelyconnected to said first shaft; a second shaft slidably and rotatablysupported in the hollow portion of said first shaft and extending fromoutside said shell through at least a portion of said chamber below saidsolid material inlet; a laterally extending table rigidly affixed tosaid second shaft below the lower lip of said inlet conduit;longitudinal displacement means operatively connected to said secondshaft for spacing said table from said inlet conduit; and second drivemeans operatively connected to said second shaft.

ROBERT BERKEMEYER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 730,782 Morrison June 9, 19031,456,165 Whitney May 22, 1923 2,417,049 Bailey et a1 Mar. 11, 19472,432,872 Ferro Dec. 16, 1947 2,432,873 Ferro et a1. Dec. 16, 19472,447,306 Bailey et a1 Aug. 17, 1948 2,468,712 Kohler Apr. 26, 19492,520,164 Norton Aug. 29, 1950

1. AN IMPROVED PEBBLE HEATER APPARATUS WHICH COMPRISES IN COMBINATION ASUBSTANTIALLY VERTICALLY DISPOSED CLOSED PEBBLE HEATER CHAMBER, SAIDCHAMBER HAVING A PEBBLE INLET AND AN EFFLUENT OUTLET CONDUIT IN ITSUPPER END PORTION, AND A GAS INLET AND A PEBBLE OUTLET IN ITS LOWER ENDPORTION; A CLOSED GAS HEATING CHAMBER HAVING A PEBBLE INLET AND ANEFFLUENT OUTLET IN ITS UPPER END PORTION AND A GAS INLET AND A PEBBLEOUTLET IN ITS LOWER END PORTION, SAID GAS HEATING CHAMBER BEING INSUBSTANTIALLY COAXIAL ALIGNMENT WITH SAID PEBBLE HEATING CHAMBER ANDSAID PEBBLE INLET OF SAID GAS HEATING CHAMBER COMMUNICATING WITH SAIDPEBBLE OUTLET OF SAID PEBBLE HEATING CHAMBER; A PEBBLE FEEDER WHICHCOMPRISES IN COMBINATION AN OUTER SHELL, A PEBBLE INLET CONDUITCOMMUNICATING WITH THE PEBBLE OUTLET CONDUIT OF SAID GAS HEATING CHAMBERAND EXTENDING DOWNWARDLY INTO THE CHAMBER WITHIN SAID SHELL, A SCREWCONVEYOR ROTATABLY MOUNTED IN SAID PEBBLE INLET CONDUIT ON A HOLLOW STEMWHICH EXTENDS UPWARDLY THROUGH THE UPPER END WALL OF SAID SHELL, TALBESUPPORT MEANS ROTATABLY EXTENDING COAXIALLY THROUGH AND OUT OF EACH ENDOF SAID HOLLOW STEM, A TABLE RIGIDLY MOUNTED ON SAID SUPPORT MEANS ANDSPACED BELOW THE OUTLET END OF SAID PEBBLE INLET CONDUIT, ELEVATIONMEANS OPERATIVELY CONNECTED TO THE UPPER END PORTION OF SAID TABLESUPPORT MEANS, REVERSIBLE-VARIABLE SPEED ROTATION MEANS OPERATIVELYCONNECTED TO SAID SCREW CONVEYOR, AND A PEBBLE OUTLET CONDUIT IN THELOWER PORTION OF SAID SHELL; GRAVITY MEASURING MEANS OPERATIVELYCONNECTED TO SAID EFFLUENT OUTLET OF SAID GAS HEATING CHAMBER AND SAIDELEVATION MEANS; FIRST TEMPERATURE MEASURING MEANS IN THE PEBBLE OUTLETOF SAID GAS HEATING CHAMBER AND OPERATIVELY CONNECTED TO SAIDREVERSIBLE-VARIABLE SPEED ROTATION MEANS; AND ELEVATOR MEANS CONNECTEDAT ITS LOWER END TO SAID PEBBLE OUTLET CONDUIT OF SAID PEBBLE FEEDER ANDAT ITS UPPER END TO SAID PEBBLE INLET CONDUIT TO SAID PEBBLE HEATERCHAMBER.